1. Field of the Invention
The present invention relates to a process for producing a clear aqueous solution of the magnesium salt of an olefin sulfonic acid. More specifically, it relates to a process for producing a clear or transparent aqueous solution containing a high concentration of the magnesium salt of an olefin sulfonic acid by rapidly neutralizing and hydrolyzing a sulfonated olefin.
2. Description of the Prior Art
The magnesium salt of an olefin sulfonic acid is preferably used as an active agent (surfactant) for a liquid detergent due to its excellent frothing property. The magnesium salt of an olefin sulfonic acid can be produced by neutralizing and hydrolyzing a sulfonated olefin in the presence of magnesium hydroxide and/or magnesium oxide. However, since the magnesium hydroxide and oxide are only slightly soluble in water, the reaction rates of the neutralization and the hydrolysis are slow and, therefore, there is a problem that acidic hydrolysis of the sulfonated products occurs in the reaction system. That is to say, in the hydrolysis process of the sulfonated olefin, sultone present in the sulfonated olefin is hydrolyzed, and the hydroxyalkane sulfonic acid and alkene sulfonic acid, which are derived from the hydrolysis of the sultone, are neutralized. However, since the dissolving rate of the alkali (i.e. magnesium hydroxide andor oxide) into water is very slow, the hydrolysis occurs in the acidic side. This is because the amount of the acids formed by the hydrolysis of the sultone (i.e. the hydrolysis rate) is larger than that of the acid which is neutralized by the alkali (i.e. the alkali dissolving rate).
Such acidic hydrilysis necessarily causes the problems that a bad odor and color deterioration are generated in the reaction product. For this reason, in order to prevent the above-mentioned acidic hydrolysis, it is considered that the sulfonated olefin be neutralized and hydrolyzed in an extremely low concentration, or the sulfonated olefin be neutralized and hydrolyzed by using a large excess of the alkali. However, in the former process only a low concentration of the olefin sulfonate is obtained. In the latter process, due to the presence of the excess alkali, the reaction product becomes opaque or unclear and, occasionally, even precipitates are formed in the reaction product. These opacity and precipitates caused by the presence of the excess alkali can be removed to a certain extent by removing the unreacted alkali by means of a filtration or by consuming the unreacted alkali with the addition of an appropriate inorganic or organic acid. However, a reaction product having a high viscosity is not easily filtered. In the case where the reaction product is diluted in order to make the filtration smooth, the concentration of the olefin sulfonate unpreferably decreased. On the other hand, there are problems in the method for removing the unreacted alkali with the addition of the additional acid after the reaction, in that not only does the operation become troublesome but, also, the extra salts are incorporated into the reaction products.